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CERES +15V Power Converter Anomaly

Bruce A. Wielicki

October 13, 1998

Yesterday at 8pm EST the CERES instrument was powered back up. Greg Stover of the CERES instrument team just called from GSFC where a joint LaRC/GSFC team are monitoring the instrument operations and real-time data as the instrument warms back up to operational temperatures.

  • So far the instrument appears to be operating nominally and the DAA +15V volt converter is still holding at its nominal value of 15V. This is now an exciting game of watching the instrument temperature rise and monitoring the response of the converter. Recall from my earlier email that we have found

    DAA +15 Voltage = 15 + 0.6 (T-Tmin)

  • Over the month of August, Tmin dropped from 20.7C to 17.2C, or 3.5C in one month (linear with time). It leveled off near 17.2C the last four days of August. If this trend of 3.5C drop every 4 weeks had continued through Sept into mid-October, then we would predict that Tmin would now have dropped to around 12C.

  • The temperature value most closely correlated with the DAA voltage is the MAM baffle temperature. Unfortunately, this temperature is not part of the real-time housekeeping data that we can monitor at GSFC or LaRC: we have to get it off the telemetry data tapes. The GSFC TRMM spacecraft operations group and the LaRC DAAC have done a great job of turning those data around quickly, so we only have about a 6 hour delay in getting the MAM temperature. As of roughly 2am EST the MAM temperature had risen to 11.4C, and was expected from earlier thermal modeling to be near 17C by 9am EST.

  • There is an additional temperature that is typically reasonably close to the MAM value, that is reported in the real time data. By 9am this temperature had risen to about 17C and we still had seen no rise in the DAA +15V output voltage. By early this afternoon we should have the actual MAM temperatures and can confirm the relationship.

  • So far, it looks like there has been no further degradation of the DAA +15V converter past that seen at the end of August.

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